1) Field of the Invention
The present invention relates to a developing device for using in an electrostatic recording apparatus, such as an electrophotographic copying machine or an electrophotographic printer, and, more specifically, to a developing device suitable for use in a multicolor electrostatic recording apparatus for multicolor recording and provided with a plurality of recording units arranged in a line.
2) Description of the Related Art
In an electrostatic recording apparatus of the type as mentioned above, an electrostatic latent image is formed on an electrostatic latent image carrying body, such as a photosensitive body or a dielectric body, the electrostatic latent image is developed electrostatically as a charged toner image using a developer, the charged toner image is transferred electrostatically to a recording medium, such as a recording sheet of paper, and then the toner image is fixed to the recording medium by heat, pressure or light.
As a multicolor recording apparatus utilizing such electrostatic recording techniques, a single-drum type of multicolor recording apparatus is known. This recording apparatus comprises a single electrostatic image carrying body, i.e., a photosensitive drum, and a plurality of developing devices using different developers containing toner of different colors, respectively, and arranged between an electrostatic image writing location at which an electrostatic latent image is written on the photosensitive drum and a transfer charger. For example, a multicolor recording apparatus for a full-color recording is provided with four developing devices, which use a yellow developer containing yellow toner, a cyan developer containing cyan toner, a magenta developer containing magenta toner, and a black developer containing black toner, respectively. First, an electrostatic latent image is formed on the photosensitive drum on the basis of yellow image data, and is developed as yellow toner image using the yellow toner, and then the yellow toner image is transferred to and fixed on a recording sheet. Subsequently, an electrostatic latent image is formed on the photosensitive drum on the basis of cyan image data, and is developed as a cyan toner image using the cyan toner, and then the cyan toner image is transferred to and fixed on the sheet of paper carrying the yellow toner image previously fixed thereto. A similar process is repeated for each of magenta image data and black image data. Consequently, the four toner images are superposed on the sheet of paper, whereby a full-color recording is made. Although the single-drum multicolor recording apparatus is advantageous in that the same has a relatively compact construction, the single-drum multicolor recording apparatus is incapable of high-speed recording, because the same needs to form the toner images of the different colors on the single photosensitive drum.
Also, as a multicolor recording apparatus for the electrostatic recording techniques, the multi-drum type of multicolor recording apparatus is known, which comprises four electrostatic recording units aligned with each other along path for moving a recording sheet of paper. The respective electrostatic recording units includes developing devices which use a developer containing yellow toner, a developer containing cyan toner, a developer containing magenta toner, and a developer containing black toner. While a recording sheet of paper is moved along the path, an yellow toner image, a cyan toner image a magenta toner image and a black toner image sequentially is formed on the sheet of paper by the four electrostatic recording devices, whereby a full-color image is obtained on the sheet of paper.
Although the multi-drum type multicolor recording apparatus as mentioned above is advantageous in that a high-speed multicolor recording can be carried out, it has the most disadvantage in that a construction thereof is large due to the alignment of the electrostatic recording units.
Especially, as a developing device incorporated in a conventional electrostatic latent recording apparatus, a type of developing device comprising a developing roller and a developer-accumulating roller side by side is well known. The developing device of this type requires a relatively large area for installation thereof. Accordingly, the multi-drum multicolor electrostatic recording apparatus utilizing a plurality of developing devices of that type also has a large construction.
Recently, there is a demand for miniaturization of various apparatuses in the information processing market. Accordingly, as various companies or makers aim at miniaturizing computers, peripheral equipments therefor, and etc., there is a strong demand for miniaturization of even a recording apparatus provided with a monochromatic developing device and occupying a small area for installation thereof. Nevertheless, the above-mentioned developing device having the developing roller and the developer-accumulating roller arranged side by side unavoidably needs a relatively large area for installation thereof.